Among the known purification processes that use free cultures of microorganisms, those using so-called “low loading” activated sludges have come into increasingly frequent use.
These methods of the “extensive” type have the feature of working with low applied mass and volumetric loadings, with high hydraulic residence times and a medium settling sludge, which leads to the construction of rather large structures, in terms of aeration tanks as well as clarification systems.
Moreover, the devices that put these conventional purification methods into practice generally require a chain of specialized units which carry out in succession the screening, sediment removal, degreasing and primary settling of the effluent to be treated, these units being positioned upstream of the step of actual biological treatment with activated sludge.
This explains why the installations of the prior art are costly, in terms of their construction as well as their operation and maintenance.